They won't because they can't. How to deal with people who aren't nice is one of the biggest flaws in anarchist theory. Because there is no way to see whether their theory of "people will all turn into nice humans without a state" is actually true.

It's basically an axiom of their ideology and some anarchists straight out reject all psychological or sociological theories that suggest humans aren't naturally good.

In my experience most anarchists either just live with the fact that violence has to be accepted (I would put Stirner into that group, for example).

Or they believe in vigilante justice. So neighbours watching and judging each other. Which only works - again - if you believe the absolute majority of people will not seek to exploit or overpower each other.